Freeze-fracture evidence of gel-phase lipid in membranes of senescing cowpea cotyledons |
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Authors: | K A Platt-Aloia W W Thomson |
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Institution: | (1) Department of Botany and Plant Sciences, University of California, 92521-0124 Riverside, CA, USA |
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Abstract: | The structural details of membrane organization in germinating and senescing cotyledons of cowpea (Vigna unguiculata (L.) Walp.) were studied by thin section and freeze-fracture electron microscopy. Germination- and senescence-related changes in the ultrastructure of parenchymal cells of cowpea cotyledons, as detected in thin sections, closely resemble those described for other leguminous seeds. Additionally, electron-dense deposits associated with the membranes, particularly the plasmalemma and endoplasmic reticulum, were seen to increase with advancing senescence. Freeze-fracture electron microscopy demonstrated that the membranes of cotyledons of 2-d-old seedings appear to be normal, with evenly dispersed intramembranous particles. However by 4 d, small areas or domains of the plasmalemma were free of intramembranous particles. These particle-free areas increased in both size and number as senescence progressed. We interpret these particle-free areas to be structural evidence for lateral phase separations of the membrane lipids into microdomains of gel-phase lipid from which intrinsic membrane proteins are excluded. Our results support wide-angle X-ray diffraction studies which have demonstrated the presence of gel-phase lipids in senescing bean cotyledons.Abbreviations EF
exoplasmic fracture
- ER
endoplasmic reticulum
- ESR
electron-spin resonance
- IMP(s)
intramembranous particle(s)
- PF
protoplasmic fracture |
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Keywords: | Lipid (gel phase) Membrane structure Microdomain Senescence (structural changes) Vigna |
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